1. Field of the Invention
This invention relates in general to a direct access storage device (DASD) of the type utilizing magnetoresistive read sensors for reading signals recorded in a magnetic medium and, more particularly, to a DASD having a novel voltage-biasing, voltage-sensing differential preamplifier for improving the high frequency bandwidth amplification of the read signal channel and providing protection of the magnetoresistive read sensor from damage due to interaction with conductive asperities.
2. Description of Related Art
Moving magnetic storage devices, especially magnetic disk drives, are the memory devices of choice. This is due to their expanded non-volatile memory storage capability combined with a relatively low cost.
Magnetic disk drives are information storage devices which utilize at least one rotatable magnetic media disk having concentric data tracks defined for storing data, a magnetic recording head or transducer for reading data from and/or writing data to the various data tracks, a slider for supporting the transducer in proximity to the data tracks typically in a flying mode above the storage media, a suspension assembly for resiliently supporting the slider and the transducer over the data tracks, and a positioning actuator coupled to the transducer/slider/suspension combination for moving the transducer across the media to the desired data track and maintaining the transducer over the data track center line during a read or a write operation. The transducer is attached to or is formed integrally with the slider which supports the transducer above the data surface of the storage disk by a cushion of air, referred to as an air-bearing, generated by the rotating disk.
Alternatively, the transducer may operate in contact with the surface of the disk. Thus, the suspension provides desired slider loading and dimensional stability between the slider and an actuator arm which couples the transducer/slider/suspension assembly to the actuator. The actuator positions the transducer over the correct track according to the data desired on a read operation or to the correct track for placement of the data during a write operation. The actuator is controlled to position the transducer over the desired data track by shifting the combination assembly across the surface of the disk in a direction generally transverse to the data tracks. The actuator may include a single arm extending from a pivot point, or alternatively a plurality of arms arranged in a comb-like fashion extending from a pivot point. A rotary voice coil motor (vcm) is attached to the rear portion of the actuator arm or arms to power movement of the actuator over the disks.
The vcm located at the rear portion of the actuator arm is comprised of a top plate spaced above a bottom plate with a magnet or pair of magnets therebetween. The vcm further includes an electrically conductive coil disposed within the rearward extension of the actuator arm and between the top and bottom plates, while overlying the magnet in a plane parallel to the magnet. In operation, current passes through the coil and interacts with the magnetic field of the magnet so as to rotate the actuator arm around its pivot and thus positioning the transducer as desired.
The magnetic media disk or disks in the disk drive are mounted to a spindle. The spindle is attached to a spindle motor which rotates the spindle and the disks to provide read/write access to the various portions on the concentric tracks on the disks.
One or more electrical conductors extend over the suspension assembly to electrically connect the read/write transducer to a read/write chip on the actuator arm. A multi line flexible printed circuit cable (actuator flex cable) provides the electrical contact between the read/write chip and the disk drive electronics which are mounted outside the disk drive housing. Inside the disk drive housing, the actuator flex cable connects to an electrical connector pin assembly, which in turn, through an opening or connector port in the housing, connects to the external electronics.
In high capacity disk drives, magnetoresistive read sensors, commonly referred to as MR heads are the prevailing read sensor because of their capability to read data from a surface of a disk at greater track and linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in resistance of its MR sensing layer (also referred to as an "MR element") as a function of the strength and direction of the magnetic flux being sensed by the MR layer.
The changes in resistance of the MR element in response to magnetic data recorded on a disk surface is amplified in the read/write chip (also referred to as the arm electronics (AE) module) on the actuator arm before transmission to the external electronics. The frequency response of the preamplifier in the AE module, and in particular its high frequency bandwidth determines the data rate capability of the disk drive. The high frequency bandwidth of the system comprising the MR element, preamplifier and interconnects is a function of the MR element resistance. MR element resistances generally have a range of values due to manufacturing variations and tolerances. The resistance of a single MR element may also change due to temperature or other conditions in the disk drive during manufacturing and use.
The MR element is known to be sensitive to and easily damaged by contacts with conductive asperities on the surface of the disk. Momentary contact of the MR element with a conductive asperity can result in transitory current flow through the MR element causing damage or destruction of the MR element. Prior differential amplifiers have applied a predetermined constant current-bias to the MR element to provide protection for the MR element. IBM's U.S. Pat. No. 4,879,610 to Jove et al., describes a protective circuit for a current-bias differential preamplifier.
A low-noise voltage-biasing differential preamplifier for MR elements is described in IBM's U.S. Pat. No. 5,204,789 to Jove et al. This prior art preamplifier only taught current-sensing of a signal produced by an MR element. Due to the relatively low values of the resistances of present and future MR elements, coupled with relatively high values of parasitic series inductance in the wiring connecting the MR element to the preamplifier, current-sensing is no longer advantageous because it would not yield higher bandwidth amplification. A further disadvantage of voltage-biasing with current-sensing is that amplitude over-equalization occurs (dR/R.sup.2) instead of the preferred dR/R amplitude equalization. Amplitude equalization techniques for systems using MR sensors are further discussed in IBM's U.S. Pat. No. 5,032,935 to Jove et al.
Therefore, it can be seen that there is need for a voltage-biasing, voltage-sensing differential preamplifier for MR elements that provides higher bandwidth amplification and provides protection from the destructive effects of contact with conductive asperities.